1. Field of the Invention
The present invention relates to a communication device used in a wireless communication system, and more particularly, to a communication device for reporting control information in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) using LTE, etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In addition, hybrid beamforming is proposed to exploit a massive antenna array, to further improve the performance of the wireless communication system. A baseband precoding and an analog beamforming may be used to realize the hybrid beamforming. The baseband precoding is related to a mapping between logical ports (e.g., data streams) and inputs of transceiver units (e.g., RF chains). The analog beamforming is related to outputs of the transceiver units and antenna elements. The UE may need to report a large amount of control information (e.g., channel state information) to the eNB, such that the eNB can operate the baseband precoding and the analog beamforming accurately (i.e., with a better performance). However, a capacity of UL control channels is usually limited, and may not be sufficient for transmitting all the control information. The transmission of the control information is thus a challenge when the hybrid beamforming is realized.
Thus, efficient reporting of the control information is an important topic to be discussed.